import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        scanner.close();
        int count = 0;
        while (n > 0) {
            count++;
            if (count % 3 == 0) {
                n -= 12;
            } else {
                n -= 2;
            }
        }
        System.out.println(count);
    }
}